Make bevy_math optional in bevy_core

Notably, this makes bevy_core, bevy_diagnostic, and bevy_asset no longer
require pulling in bevy_math. None of these crates directly depend on
the math primitives, so this is a net positive for use outside of bevy,
which can now use these crates without pulling in bevy_math and glam.

crates/bevy_core/Cargo.toml

@@ -8,16 +8,21 @@ repository = "https://github.com/bevyengine/bevy"
 license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
+[features]
+bevy = ["bevy_math", "bevy_reflect/bevy"]
 
 [dependencies]
 # bevy
 bevy_app = { path = "../bevy_app", version = "0.5.0" }
 bevy_derive = { path = "../bevy_derive", version = "0.5.0" }
 bevy_ecs = { path = "../bevy_ecs", version = "0.5.0" }
-bevy_math = { path = "../bevy_math", version = "0.5.0" }
-bevy_reflect = { path = "../bevy_reflect", version = "0.5.0", features = ["bevy"] }
+bevy_math = { path = "../bevy_math", version = "0.5.0", optional = true }
+bevy_reflect = { path = "../bevy_reflect", version = "0.5.0" }
 bevy_tasks = { path = "../bevy_tasks", version = "0.5.0" }
 bevy_utils = { path = "../bevy_utils", version = "0.5.0" }
 
 # other
 bytemuck = "1.5"
+
+[dev-dependencies]
+bevy_math = { path = "../bevy_math", version = "0.5.0" }

crates/bevy_core/src/lib.rs

@@ -66,6 +66,7 @@ impl Plugin for CorePlugin {
             .add_system_to_stage(CoreStage::PostUpdate, entity_labels_system);
 
         register_rust_types(app);
+        #[cfg(feature = "bevy_math")]
         register_math_types(app);
     }
 }
@@ -90,6 +91,7 @@ fn register_rust_types(app: &mut App) {
         .register_type::<Option<String>>();
 }
 
+#[cfg(feature = "bevy_math")]
 fn register_math_types(app: &mut App) {
     app.register_type::<bevy_math::IVec2>()
         .register_type::<bevy_math::IVec3>()

crates/bevy_internal/Cargo.toml

@@ -48,7 +48,7 @@ bevy_ci_testing = ["bevy_app/bevy_ci_testing"]
 # bevy
 bevy_app = { path = "../bevy_app", version = "0.5.0" }
 bevy_asset = { path = "../bevy_asset", version = "0.5.0" }
-bevy_core = { path = "../bevy_core", version = "0.5.0" }
+bevy_core = { path = "../bevy_core", version = "0.5.0", features = ["bevy"] }
 bevy_derive = { path = "../bevy_derive", version = "0.5.0" }
 bevy_diagnostic = { path = "../bevy_diagnostic", version = "0.5.0" }
 bevy_ecs = { path = "../bevy_ecs", version = "0.5.0" }